Even with all the setbacks from recessions, burst bubbles and vanishing industries, the United States has still pumped out breathtaking riches over the last three and half decades.

The real economy more than doubled in size; the government now uses a substantial share of that bounty to hand over as much as $5 trillion to help working families, older people, disabled and unemployed people pay for a home, visit a doctor and put their children through school.

Yet for half of all Americans, their share of the total economic pie has shrunk significantly, new research has found.

This group — the approximately 117 million adults stuck on the lower half of the income ladder — “has been completely shut off from economic growth since the 1970s,” the team of economists found. “Even after taxes and transfers, there has been close to zero growth for working-age adults in the bottom 50 percent.”

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The new findings, by the economists Thomas Piketty, Emmanuel Saez and Gabriel Zucman, provide the most thoroughgoing analysis to date of how the income kitty — like paychecks, profit-sharing, fringe benefits and food stamps — is divided among the American population.

The Income Gap Continues to Widen

Since 1980, the share of total income going to the top 1 percent of earners has doubled, while the bottom half’s share has narrowed. Stagnant wages for many Americans are a major culprit. In three and a half decades, their incomes have barely changed while those at the top have tripled. The source of that income gain has also shifted at the top; more is coming from returns on investments rather than wages. That makes it harder for the bottom half, with much less capital, to catch up.

Share of pre-tax national income

25

%

BOTTOM 50%:

20.2%

19.9%

20

15

12.5%

10

TOP 1%:

10.7%

5

0

’70

1980

’90

’00

’10

2014

Real average pre-tax income, adjusted for inflation

$1,500,000

2014 constant dollars

1,200,000

$1,304,800

900,000

TOP 1%:

600,000

$428,200

300,000

BOTTOM 50%:

$16,000

$16,200

0

’70

1980

’90

’00

’10

2014

Top 1% share of national income

12

%

11.0%

10

9.2%

8

FROM CAPITAL:

6.0%

6

4

FROM LABOR:

4.7%

2

’70

1980

’90

’00

’10

2014

Note: Income figures are for individual adults; incomes within married couples are split equally.

Source: Thomas Piketty, Emmanuel Saez and Gabriel Zucman | By Karl Russell/The New York Times

Stagnant wages have sliced the share of income collected by the bottom half of the population to 12.5 percent in 2014, from 20 percent of the total in 1980. Where did that money go? Essentially, to the top 1 percent, whose share of the nation’s income nearly doubled to more than 20 percent during that same 34-year period.

Inequality has been a defining national issue for nearly a decade, thanks in part to groundbreaking research done by Mr. Piketty at the Paris School of Economics and Mr. Saez at the University of California, Berkeley.

But now a new administration in Washington is promising to reshape the government’s role in curbing the intense concentration of wealth at the top and improving the fortunes of those left behind.

During his tenure in the White House, President Obama pushed to address income stagnation by shifting more of the tax burden from the middle class to the rich and expanding public programs like universal health insurance.

Both strategies are now targeted by President-elect Donald J. Trump and Republicans in Congress, led by House Speaker Paul Ryan. Like many conservatives, Mr. Ryan argues that aid to the poor is ultimately counterproductive because it undermines the incentive to work. Proposals put forward by Republican leaders, though short on details, make clear that they want to roll back benefits like Medicaid and the Affordable Care Act, which primarily help the poor, and direct the largest tax cuts to the wealthiest Americans.

About 30 percent of the country’s income is channeled to federal, state and local taxes. Apart from military spending and performing basic public services, much of that is distributed back to individuals through various programs and tax benefits in the form of Social Security checks, Medicare benefits and veterans’ benefits. But until now, no one has truly measured the full impact that tax payments, government spending, noncash benefits and nontaxable income together have on inequality.

Abundant documentation of income inequality already exists, but it has been challenged as incomplete. Studies have excluded the impact of taxes and value of public benefits, skeptics complained, or failed to account for the smaller size of households over time.

This latest project tries to address those earlier criticisms. What the trio of economists found is that the spectacular growth in incomes at the peak has so outpaced the small increase at the bottom from public programs intended to ameliorate poverty and inequality that the gap between the wealthiest and everyone else has continued to widen.

Average incomes, adjusted for inflation, grew by 61 percent from 1980 to 2014. But nearly $7 out of every additional $10 went to those in the top tenth of the income scale.

Inequality has soared over that period. In 1980, the researchers found, someone in the top 1 percent earned on average the equivalent of $428,200 a year in 2014 dollars — about 27 times more than the typical person in the bottom half, whose annual income equaled $16,000.

Photo

A doctor’s waiting room in Mayaguez, Puerto Rico. Residents of the island, which is struggling with a financial crisis, have endured pension cuts and cuts in Medicaid and Medicare programs.CreditDennis M. Rivera Pichardo for The New York Times

By 2014, the average income of half of American adults had barely budged, remaining around $16,000, while members of the top 1 percent brought home, on average, $1,304,800 or 81 times as much.

That ratio, the authors point out, “is similar to the gap between the average income in the United States and the average income in the world’s poorest countries, the war-torn Democratic Republic of Congo, Central African Republic and Burundi.”

The growth of incomes has probably increased a bit since 2014, the latest year for which full data exists, said Mr. Zucman, who, like Mr. Saez, also teaches at the University of California, Berkeley. But it is “not enough to make any significant difference to our long-run finding, and in particular, to affect the long-run stagnation of bottom-50-percent incomes.”

He was to present the findings at a close-door workshop at the City University of New York on Tuesday.

Tax credits and programs like Medicare and disability payments have helped families at the lower half of the income scale. But they have just nipped at the heels of the underlying trend.

“It confirms the surge in income at the top,” said Raj Chetty, an economist at Stanford unaffiliated with the project, who called the work “terrific and very important. And it shows government redistribution doesn’t really change the picture.”

Lawrence Katz, an economist at Harvard who also independently reviewed the research, agreed that the data underscored the inadequacies of programs that try to redress inequities after the fact. “It suggests that if you don’t do something earlier in the market, before distribution, through better education or greater bargaining power, it’s really tough to offset completely,” Mr. Katz said. “Countries with less inequality do some of both.”

Mr. Katz and Claudia Goldin, a Harvard economist, have argued that advances in technology, while crucial to improving productivity and generating economic growth, also have exacerbated inequality by driving down wages of low-skilled workers. The rewards of education are greater than they have ever been, but advancement nationwide has slowed and the system confers many of its favors on the children of the affluent.

If there is a bright spot in the new comprehensive research, it is that after taxes and government spending, the middle class is in better shape than previous studies had shown. That earlier research had missed growth in nontaxable income like employee benefits. “The real income of the middle class is a bit better than we thought,” Mr. Katz said.

As troubling as some may find inequality, it is not necessarily the fault of a rigged system, said N. Gregory Mankiw, an economist at Harvard who is familiar with the new research. He argues that large disparities in income more often than not accurately reflect widely varying economic contributions.

“Inequality is a symptom of a variety of things,” Mr. Mankiw said. Technological progress may be a cause, but it benefits society over all, whereas the weakness of the educational system is clearly negative.

Edward Conard, the author of “The Upside of Inequality” and a former business partner of Mitt Romney, agreed. “People say this is zero-sum game, and you’re taking money that would have gone to the other 50 percent,” he said. “That’s not what happened.”

Instead, Mr. Conard said, entrepreneurs in the United States have been willing to take big risks that have helped foster an infrastructure that promotes innovation, not just in Silicon Valley but in many other growing places around the country. “When rewards go up, people are more inclined to take risks,” he said. Some of those risks pay off and create wealth for everyone.

The new research challenges that contention, at least in part.

Mr. Piketty, Mr. Saez and Mr. Zucman concluded that the main driver of wealth in recent years has been investment income at the top. That is a switch from the 1980s and 1990s, when gains in income were primarily generated by working.

That divergence can slow innovation and further entrench inequities, said Heather Boushey, an economist at the Washington Center for Equitable Growth. When labor income provides the primary route to riches, it creates incentives for people to improve their education and work harder, Ms. Boushey explained. But if getting ahead requires already having a stockpile of cash or inheriting a windfall from your parents, then it is much harder to work your way up.

“If you’re closing off entryways, then you are basically shutting off avenues to competitiveness, innovation and growth,” Ms. Boushey said, “even if you don’t care about fairness.”

Correction: December 6, 2016

Because of an editing error, an earlier version of this article misspelled the surname of the author of “The Upside of Inequality” on second reference. As correctly noted on first reference, he is Edward Conard, not Conrad. In addition, an earlier version of a chart showing the sources of income for the top 1 percent had labels for labor and capital reversed.

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When I was a very young man I had an incredible grandmother named Sarah Elizabeth Walters. She told me the following words: "Son don't let the grass grow under your feet." I took those words to heart and went out to see the world. My life has been ana adventure all over the world. I have lived on six of the seven continents. I have been lucky to live this long.